After World War II, the Soviet Union jumped into the nuclear arms race with both feet. A plant was built in a secret city named Chelyabinsk-40 to produce plutonium. Between 1948 and 1990, a million residents of the Chelyabinsk Province in Russia found out what happens when radioactive waste is not properly stored or cooled -not that they were told what was happening.

Thirty-nine years of effluent had saturated the lake with nasty isotopes, including an estimated 120 megacuries of long-lived radiation. In contrast, the Chernobyl incident released roughly 100 megacuries of radiation into the environment, but only about 3 megacuries of Strontium-90 and Cesium-137. A delegation who visited Lake Karachay in 1990 measured the radiation at the point where the effluent entered the water, and the needles of their Geiger counters danced at about 600 Röntgens per hour–enough to provide a lethal dose in one hour. They did not linger long.

The Worldwatch Institute calls it the “most polluted spot” in history. Damn Interesting has the story. Link